Medical device including a solderable linear elastic nickel-titanium distal end section and methods of preparation therefor

ABSTRACT

Shapeable guide wire devices and methods for their manufacture. Guide wire devices include an elongate shaft member having a shapeable distal end section that is formed from a linear pseudoelastic nickel-titanium (Ni—Ti) alloy that has linear pseudoelastic behavior without a phase transformation or onset of stress-induced martensite. Linear pseudoelastic Ni—Ti alloy, which is distinct from non-linear pseudoelastic (i.e., superelastic) Ni—Ti alloy, is highly durable, corrosion resistant, and has high stiffness. The shapeable distal end section is shapeable by a user to facilitate guiding the guide wire through tortuous anatomy. In addition, linear pseudoelastic Ni—Ti alloy is more durable tip material than other shapeable tip materials such as stainless steel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of Ser. No. 15/670,761, filed Aug. 7,2017, which is a continuation of U.S. patent application Ser. No.13/172,278, filed 29 Jun. 2011, now U.S. Pat. No. 9,724,494, thedisclosure of which is incorporated herein by reference in its entirety.

BACKGROUND 1. The Field of the Invention

The present invention relates to guide wires, particularly to guidewires used to guide a catheter in a body lumen such as a blood vessel.

2. The Relevant Technology

Guide wires are used to guide a catheter for treatment of intravascularsites, such as percutaneous transluminal coronary angioplasty (“PTCA”),or in examination such as cardio-angiography. A guide wire used in thePTCA is inserted into the vicinity of a target angiostenosis portiontogether with a balloon catheter, and is operated to guide the distalend portion of the balloon catheter to the target angiostenosis portion.

A guide wire needs appropriate flexibility, pushability and torquetransmission performance for transmitting an operational force from theproximal end portion to the distal end, and kink resistance (resistanceagainst sharp bending). To meet such requirements, superelasticmaterials such as a Ni—Ti alloy and high strength materials have beenused for forming a core member (i.e., a wire body) of a guide wire.

Near equiatomic binary nickel-titanium alloys are known to exhibit“pseudoelastic” behavior when given certain cold working processes orcold working and heat treatment processes following hot working.Pseudoelasticity can be further divided into two subcategories: “linear”pseudoelasticity and “non-linear” pseudoelasticity. “Non-linear”pseudoelasticity is sometimes used by those in the industry synonymouslywith “superelasticity.”

Linear pseudoelasticity typically results from cold working. Non-linearpseudoelasticity results from cold working and subsequent heattreatment. Non-linear pseudoelasticity, in its idealized state, exhibitsa relatively flat loading plateau in which a large amount of recoverablestrain is possible with very little increase in stress. This flatplateau can be seen in the stress-strain hysteresis curve of the alloy.Linear pseudoelasticity exhibits no such flat plateau. Non-linearpseudoelasticity is known to occur due to a reversible phasetransformation from austenite to martensite, the latter more preciselycalled stress-induced martensite (“SIM”). Linear pseudoelastic materialsexhibit no such phase transformation. Linear pseudoelastic nickeltitanium alloy can be permanently deformed or shaped by overstressingthe alloy above a plateau stress that is at least partially dependent onthe amount of cold-worked martensite structure present in the linearpseudoelastic structure. This is in marked contrast to non-linearpseudoelastic nickel titanium alloy, which cannot be permanentlydeformed by overstressing.

BRIEF SUMMARY

The present disclosure describes guide wire devices and methods fortheir manufacture. Guide wire devices described herein include anelongate shaft member having a shapeable distal end section that isformed from a linear pseudoelastic nickel-titanium (Ni—Ti) alloy thathas linear pseudoelastic behavior without a phase transformation oronset of stress-induced martensite. Linear pseudoelastic Ni—Ti alloy,which is distinct from non-linear pseudoelastic (i.e., superelastic)Ni—Ti alloy, is highly durable, corrosion resistant, and has highstiffness. The shapeable distal end section is shapeable by a user tofacilitate guiding the guide wire through tortuous anatomy. In addition,linear pseudoelastic Ni—Ti alloy is more durable tip material than othershapeable tip materials such as stainless steel. This may, for example,allow practitioners to use one wire to treat multiple lesions,potentially reducing costs and procedure time.

In one embodiment, a shapeable guide wire device is described. Theshapeable guide wire device includes an elongate shaft member thatincludes a proximal end section and a shapeable distal end sectionhaving a solder material applied thereto, wherein the shapeable distalend section includes a cold-worked nickel titanium alloy exhibitinglinear pseudoelasticity. The shapeable guide wire device furtherincludes a helical coil section disposed about at least the shapeabledistal end section and an atraumatic cap section attached to the helicalcoil section and the solder material of the shapeable distal end sectionvia a soldered joint. According to the present disclosure, the solderedjoint is formed without substantial loss of the linear pseudoelasticityof the shapeable distal end section.

In another embodiment, a method for fabricating a guide wire device isdisclosed. The method includes (1) fabricating an elongate shaft memberthat includes a proximal end section and a distal end section. In oneembodiment, the distal end section includes a distal nickel-titaniumalloy member that has a first cross-sectional dimension. The methodfurther includes (2) applying a solder material to at least a portion ofthe distal end section, (3) cold working at least a portion of thedistal end section having the solder material applied thereto, whereinthe cold working yields a distal shapeable end section having a secondcross-sectional dimension and linear pseudoelastic deformation behavior,and (4) soldering the distal shapeable section and a helical coilsection disposed about the distal shapeable section to an atraumatic capwithout substantial loss of the linear pseudoelasticity of the distalshapeable section.

In one embodiment, fabricating an elongate shaft member that includes aproximal end section and a distal end section may include attaching(e.g., by welding) a proximal end section fabricated from a firstmaterial such as stainless steel to a distal end section fabricated froma second material such as nickel-titanium alloy. Alternatively, theelongate shaft member can be fabricated from a single material such as,but not limited to, a nickel-titanium alloy.

In one embodiment, fabricating an elongate shaft member may furtherinclude drawing at least a portion of the elongate shaft member througha drawing die, rolling, calendaring, or grinding to form or reshape theat least a portion of the elongate shaft member and cleaning theelongate shaft member such as by ultrasonically cleaning.

Ni—Ti alloys, such as those described herein, are very difficult tosolder due to the formation of a tenacious, naturally occurring oxidecoating which prevents the molten solder from wetting the surface of thealloy. It has been found that by first treating the surface of therefractory superelastic alloy with molten alkali metal hydroxide, e.g.,sodium, potassium, lithium or mixtures thereof to form a nascent alloysurface and then pretinning (i.e., applying a suitable solder material,such as, a gold-tin solder, a gold-indium solder, a gold-germaniumsolder, a silver-tin solder, a silver-gold-tin solder, or anothersuitable solder) without contacting air, that Ni—Ti alloys can bereadily soldered in a conventional manner. In one embodiment, solder canbe applied to at least a portion of the distal end section by dippingthe at least the distal end section into a bath of a molten soldermaterial, wherein the bath of molten solder material includes an upperlayer of a molten metal hydroxide and a lower layer of the molten soldermaterial.

Subsequently, at least a portion of the distal end section, with thesolder material applied thereto, can be cold-worked to yield a distalshapeable end section having a second cross-sectional dimension. Afterapplying the solder material and cold working, a helical coil sectioncan be assembled around the a distal portion of the elongate shaftmember, including the distal shapeable section, and a rounded plug(i.e., an aturaumatic cap section) can be formed at the distal end ofthe assembly by soldering the distal shapeable section and a helicalcoil section disposed about the distal shapeable section to the roundedplug without substantial loss of the linear pseudoelasticity of thedistal shapeable section. The pretinning followed by cold working andforming the atraumatic cap at the distal end of the elongate shaftmember yields a user-shapeable distal end section that exhibits linearpseudoelastic deformation behavior without a phase transformation oronset of stress-induced martensite.

In a more specific embodiment, a method for fabricating a guide wiredevice that has a shapeable distal end section is disclosed. The methodincludes (1) providing an elongate shaft member that includes a proximalend section and a distal end section, wherein the distal end sectionincludes a nickel-titanium alloy member, (2) grinding at least a portionof the distal end section to a first cross-sectional dimension, and (3)ultrasonically cleaning at least the distal end section. After grindingand cleaning, the method further includes (4) dipping at least a portionof the distal end section into a bath of a molten solder material,wherein the bath of molten solder material includes an upper layer of amolten metal hydroxide and a lower layer of the molten solder material,and (5) cold working at least a portion of the distal end section,wherein the cold working yields a distal shapeable section having alinear pseudoelastic nickel-titanium microstructure. After cold workingat least a portion of the distal end section, the method continues with(6) ultrasonically cleaning at least the distal end section, (7)disposing a helical coil section about the distal shapeable section, and(8) forming an atraumatic cap section coupling the helical coil sectionand the distal shapeable section via a soldered joint, wherein thesoldered joint is formed without loss of the linear elasticnickel-titanium microstructure.

These and other objects and features of the present disclosure willbecome more fully apparent from the following description and appendedclaims, or may be learned by the practice of embodiments of theinvention as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of thepresent disclosure, a more particular description of the embodiments ofthe invention will be rendered by reference to the appended drawings. Itis appreciated that these drawings depict only illustrated embodimentsof the invention and are therefore not to be considered limiting of itsscope. The embodiments of the invention will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1A illustrates a partial cut-away view of a guide wire deviceaccording to one embodiment of the present invention;

FIG. 1B illustrates an enlarged view of a distal end portion of theguide wire device illustrated in FIG. 1A;

FIG. 2 illustrates stress-strain curves for stainless steel, a linearpseudoelastic Ni—Ti alloy, and a superelastic (i.e., non-linearpseudoelastic) Ni—Ti alloy;

FIG. 3 is a diagram schematically illustrating the relationship betweendegree of cold work and shapeability of a Ni—Ti alloy;

FIG. 4 is a diagram illustrating the yield stress of samples of Ni—Tialloy having various degrees of cold work; and

FIG. 5 is a diagram illustrating loss of linear pseudoelastic characterof Ni—Ti alloy as a result of moderate heat exposure for varying amountsof time.

DETAILED DESCRIPTION I. Introduction

The present disclosure describes guide wire devices and methods fortheir manufacture. Guide wire devices disclosed herein include anelongate shaft member having a shapeable distal end section that isformed from a linear pseudoelastic nickel-titanium (Ni—Ti) alloy thathas linear pseudoelastic behavior without the onset of stress-inducedmartensite during deformation. Linear pseudoelastic Ni—Ti alloy, whichis distinct from non-linear pseudoelastic (i.e., superelastic) Ni—Tialloy, is highly durable, corrosion resistant, and has a relatively highstiffness. Linear pseudoelastic Ni—Ti is in the martensite phase at bodytemperature (e.g., about 37° C.); in contrast, superelastic Ni—Ti usedfor medical devices is typically manufactured in the austenite phase atbody temperature and superelastic Ni—Ti experiences an austenite tomartensite phase transformation when stressed. The shapeable distal endsection is shapeable by a user to facilitate guiding the guide wirethrough tortuous anatomy. In addition, linear pseudoelastic Ni—Ti alloyis more durable tip material than other shapeable tip materials, such asstainless steel. This may, for example, allow practitioners to use onewire to treat multiple lesions, potentially reducing costs and proceduretime.

Guide wire devices are used in minimal invasive procedures such as, butnot limited to, percutaneous transluminal coronary angioplasty (PTCA) totrack through vessels, access and cross lesions, and supportinterventional devices for a variety of procedures. Because they aredesigned to track through a patient's vasculature, for example, guidewire devices may be quite long (e.g., about 150 cm to about 300 cm inlength) and thin. Guide wire devices need to be long enough to travelfrom an access point outside a patient's body to a treatment site andnarrow enough to pass freely through the patient's vasculature. Forexample, a typical guide wire device has an overall diameter of about0.2 mm to about 0.5 mm for coronary use (e.g., about the diameter of thepencil leads typically used in automatic pencils). Larger diameter guidewires may be employed in peripheral arteries and other body lumens. Thediameter of the guide wire device affects its flexibility, support, andtorque. Thinner wires are more flexible and are able to access narrowervessels while larger diameter wires offer greater support and torquetransmission.

II. Guide Wire Devices

In one embodiment of the present invention, a shapeable guide wiredevice is described. The shapeable guide wire device includes anelongate shaft member that includes a proximal end section and ashapeable distal end section having a solder material applied thereto.The shapeable distal end section includes a cold-worked linearnickel-titanium alloy exhibiting linear pseudoelastic deformationbehavior imparted by cold work. The shapeable guide wire device furtherincludes a helical coil section disposed about at least the shapeabledistal end section, and an atraumatic cap section that is attached to(e.g., soldered to) the helical coil section and the shapeable distalend section. The atraumatic cap section may be formed from a bead ofsolder material that is applied to the helical coil section and theshapeable distal end section. According to the present embodiment, theatraumatic cap section is attached to the helical coil and the distalend section without loss of the linear elastic nickel-titaniummicrostructure.

Referring now to FIG. 1A, a partial cut-away view of a guide wire device100 according to an embodiment of the invention is illustrated. Theguide wire device 100 may be adapted to be inserted into a patient'sbody lumen, such as an artery. The guide wire device 100 includes anelongated proximal portion 102 and a distal portion 104. In oneembodiment, the elongated proximal portion 102 may be formed from afirst material such as stainless steel (e.g., 316L stainless steel) or aNi—Ti alloy and the distal portion may be formed from a second materialsuch as a Ni—Ti alloy. In another embodiment, the elongated proximalportion 102 and the distal portion 104 may be formed from a singlematerial, such as a Ni—Ti alloy. If the elongated proximal portion 102and the distal portion 104 are formed from different materials, theelongated proximal portion 102 and the distal portion 104 may coupled toone another via a welded joint 116 or another joint such as an adhesivejoint, a brazed joint, or another suitable joint that couples theproximal portion 102 and the distal portion 104 into a torquetransmitting relationship.

The distal portion 104 has at least one tapered section 106 that becomessmaller in diameter in the distal direction. The length and diameter ofthe tapered distal core section 106 can, for example, affect thetrackability of the guide wire device 100. Typically, gradual or longtapers produce a guide wire device with less support but greatertrackability, while abrupt or short tapers produce a guide wire devicethat provides greater support but also greater tendency to prolapse(i.e., kink) when steering.

The tapered distal core section 106 further includes a shapeable distalend section 108 that is formed from a Ni—Ti alloy in a linearpseudoelastic state. As will be discussed in greater detail below, thelinear pseudoelastic state can be imparted upon Ni—Ti alloy by coldwork. With increasing cold work, the elastic modulus of the linearsection of the stress-strain curve increases, imparting differentdegrees of linear pseudoelasticity. Linear pseudoelastic Ni—Ti canreadily be permanently deformed by stressing the material beyond itselastic strain limit. As such, the shapeable distal end section 108 canallow a practitioner to shape the distal and of the guide wire device100 to a desired shape (e.g., a J-bend) for tracking through thepatient's vasculature.

The Ni—Ti alloy portion(s) of the guide wire device 100 discussedherein, e.g., the distal portion 104, are, in some embodiment, made ofan alloy material that includes about 30 to about 52% titanium and abalance nickel. The alloy may also include up to about 10% of one ormore other alloying elements. The other alloying elements may beselected from the group consisting of iron, cobalt, vanadium, platinum,palladium and copper. The alloy can contain up to about 10% copper andvanadium and up to 3% of the other alloying elements. Cold worked Ni—Tialloy portions (e.g., the shapeable distal end section 108) exhibitlinear pseudoelastic behavior that is in the martensite phase withoutthe appearance of stress-induced martensite upon deformation.

In one embodiment, the shapeable distal end section 108 is manufacturedby, for example, drawing and grinding the distal end of the Ni—Ti distalsection 104 to a first cross-sectional dimension, applying a soldermaterial to the distal section 104, and cold-working (e.g., byflattening) the ground portion to a second cross-sectional dimension. Inanother embodiment, the shapeable distal end section 108 is manufacturedby, for example, drawing and grinding the distal end of the Ni—Ti distalsection 104 to a first cross-sectional dimension (e.g., a thickness or adiameter), cold-working a first time, applying a solder material to thedistal section 104, and cold-working a second time (e.g., by flattening)the ground portion to a second cross-sectional dimension (e.g., athickness). If cold working is performed prior to applying the soldermaterial, it may be desirable to use a solder material with asufficiently low melting temperature (e.g., as low as about 150° C.)such that a minimal amount of cold work is lost due to exposure to themolten solder.

The first dimension can be in a range from about 0.1 mm to about 0.07mm, or about 0.08 mm. The second cross-sectional dimension, which isformed by, for example, cold-work flattening at least a part of theground distal section, is in a range from about 0.065 mm to about 0.008mm, about 0.055 mm to about 0.03 mm, about 0.05 to about 0.04 mm, orabout 0.045 mm. In other words, the shapeable distal end section 108 ismade from a Ni—Ti alloy that exhibits linear pseudoelastic deformationbehavior imparted by about 20% to about 90% cold work, about 25% toabout 65% cold work, about 40% cold work to about 50% cold work, orabout 45% cold work.

The length of the shapeable distal end section 108 can, for example,affect the steerability of the guide-wire device 100. In one embodiment,the shapeable distal end section 108 is about 1 cm to about 10 cm inlength, about 2 cm to about 6 cm in length, about 2 cm to about 4 cm inlength, or about 2 cm in length.

As illustrated in FIG. 1A, the guide wire device 100 includes a helicalcoil section 110. The helical coil section 110 affects support,trackability, and visibility of the guide wire device and providestactile feedback. In some embodiments, the most distal section of thehelical coil section 110 is made of radiopaque metal, such as platinumor platinum-nickel alloys, to facilitate the observation thereof whileit is disposed within a patient's body. The helical coil section 110 isdisposed about all or only a portion of the distal portion 104 and theshapeable distal end section 108, and has a rounded, atraumatic capsection 120 on the distal end thereof. In some embodiments, theatraumatic cap section 120 is formed from a bead of solder applied tothe helical coil section 110 and the shapeable distal end section 108.Typical solder materials that can be used for forming the atraumatic capsection 120 include 80/20 gold-tin or 95/5 silver-tin. However, othersuitable types of medical-grade, lead-free solder can be used. Thehelical coil section 110 is secured to the distal portion 104 atproximal location 114 and at intermediate location 112 by a suitablesolder material and/or a suitable adhesive.

Referring now to FIG. 1B, a cut-away view of an enlarged portion of thedistal end of the guide wire device 100 is illustrated. The portion ofthe guide wire device 100 illustrated in FIG. 1B shows the tapereddistal section 106, the shapeable distal end section 108, the helicalcoil section 110, and the atraumatic cap 120. The shapeable distal endsection 108 includes a distal wire portion 124 composed of a Ni—Ti alloythat extends from the tapered distal section 106. As illustrated, thedistal wire portion is coated with a layer of solder material 126 (e.g.,a gold-tin solder, a gold-indium solder, a gold-germanium solder, asilver-tin solder, a silver-gold-tin solder, or another suitablesolder). At least a portion of the distal wire portion 124 is coldworked after application of the layer of solder material 126 in order toform the shapeable distal end section 108.

The helical coil section 110 is attached to the shapeable distal endsection 108 by soldering the rounded, atraumatic cap section 120 ontothe helical coil section 110 and the shapeable distal end section 108.As illustrated, a portion 110 a of the helical coil section 110 isembedded in the atraumatic cap 120, thus attaching the atraumatic cap120 to the helical coil 120. The atraumatic cap 120 forms a solderedjoint 122 with the shapeable distal end section 108 by forming a solderbond with the layer of solder material 126 that is in turn bonded to thedistal wire portion 124. Because Ni—Ti alloy forms a persistent oxidelayer, it can be difficult to solder Ni—Ti. Methods of manufacture willbe discussed in detail below. However, because the distal wire portion124 has a layer of solder material 126 bonded thereto, the atraumaticcap 120 can readily form a joint 122 with the shapeable distal endsection 108. By using the methods and procedures described herein, theatraumatic cap 120 can be soldered to or formed on the shapeable distalend section 108 without significant loss of the linear pseudoelasticnickel-titanium deformation behavior.

In one embodiment, portions of the guide wire device 100 are coated witha coating 118 of lubricous material such as polytetrafluoroethylene(PTFE) (sold under the trademark Teflon by du Pont, de Nemours & Co.) orother suitable lubricous coatings such as the polysiloxane coatings,polyvinylpyrrolidone (PVP), and the like.

The guide wire device 100 that includes a Ni—Ti alloy portion 104 with ashapeable distal end section 108 having linear pseudoelasticcharacteristics, which facilitates shaping of the distal tip section 108of the guide wire 100. The Ni—Ti alloy portion 104 may also include asuperelastic portion proximal to the shapeable distal end section 108 tofacilitate the advancing of the guide wire in a body lumen. The linearpseudoelastic and superelastic portions exhibit extensive, recoverablestrain, which greatly minimizes the risk of damage to arteries duringthe advancement therein.

The proximal portion 102 of the guide wire device 100 is typically madefrom stainless steel. Stainless steel is generally significantlystronger, i.e., higher yield strength and ultimate tensile strength,than superelastic or linear pseudo elastic Ni—Ti. Suitable high strengthmaterials include 304 or 316L stainless steel, which is a conventionalmaterial in guide wire construction.

To illustrate the foregoing points, FIG. 2 contains the elasticcomponent of three idealized stress-strain curves for 316L stainlesssteel 222, linear pseudoelastic Ni—Ti 218/220, and non-linearpseudoelastic Ni—Ti alloy 200. The stress/strain relationship is plottedon x-y axes, with the x axis representing strain and the y axisrepresenting stress.

In curve 200, when stress is applied to a specimen of a Ni—Ti alloyexhibiting non-linear pseudoelastic characteristics at a temperature ator above where the materials is in the austenitic phase, the specimendeforms elastically in region 202 until it reaches a particular stresslevel where the alloy then undergoes a stress-induced phasetransformation from the austenitic phase to the martensitic phase (i.e.,the stress-induced martensite phase). As the phase transformationprogresses, the alloy undergoes significant increases in strain withlittle or no corresponding increases in stress. On curve 200, this isrepresented by the upper, nearly flat stress plateau 204. The strainincreases while the stress from continued deformation remainsessentially constant until the transformation of the austenitic phase tothe martensitic phase is complete at approximately region 206.Thereafter, further increase in stress is necessary to cause furtherdeformation to point 208. The martensitic metal first yields elasticallyupon the application of additional stress and then plastically withpermanent deformation (not shown).

If the load on the specimen is removed before any permanent deformationhas occurred, the martensitic Ni—Ti alloy elastically recovers andtransforms back to the austenitic phase. The reduction in stress firstcauses a decrease in strain along region 210. As stress reductionreaches the level at which the martensitic phase transforms essentiallycompletely back into the austenitic phase at region 212, the stresslevel in the specimen remains essentially constant to continue relievingstrain along lower plateau 214 (but less than the constant stress levelat which the austenitic crystalline structure transforms to themartensitic crystalline structure until the transformation back to theaustenitic phase is complete); i.e., there is significant recovery instrain with only negligible corresponding stress reduction.

After the transformation back to austenite is complete, further stressreduction results in elastic strain reduction along region 216. Thisability to incur significant strain at relatively constant stress uponthe application of a load and to recover from the deformation upon theremoval of the load is commonly referred to as non-linearpseudoelasticity (or superelasticity).

FIG. 2 also includes a curve 218/220 representing the idealized behaviorof linear pseudoelastic Ni—Ti alloy as utilized in the shapeable distalend section 108 in the present invention. The slope of curve 218/220generally represents the Young's modulus of the linear pseudoelasticNi—Ti alloy. Also, curve 218/220 does not contain any flat plateaustresses found in curve 200. This stands to reason since the Ni—Ti alloyof curve 218-220 remains in the martensitic phase throughout and doesnot undergo any phase change. To that end, curve 218/220 shows thatincreasing stress begets a proportional increase in reversible strain,and a release of stress begets a proportional decrease in strain. Theareas bounded by curves 200 and 218-220 represent the hysteresis in theNi—Ti alloy.

As is apparent from comparing curve 218/220 to curve 200 in FIG. 2 ,with the use of linear pseudoelastic Ni—Ti alloy, the mechanicalstrength of linear pseudoelastic Ni—Ti alloy and non-linearpseudoelastic Ni—Ti alloy is similar. Consequently, a major benefit ofthe distal end section 108 made from linear pseudoelastic Ni—Ti alloy isthat it is shapeable, whereas a distal end section made from non-linearpseudoelastic Ni—Ti alloy is practically un-shapeable because it is verydifficult to overstrain non-linear pseudoelastic Ni—Ti alloy.

FIG. 2 also includes curve 220 which is the elastic behavior of astandard 316L stainless steel. Stress is incrementally applied to thesteel and, just prior to the metal deforming plastically, decrementallyreleased.

III. Methods for Fabricating a Guide Wire Device

In one embodiment, a method for fabricating a guide wire device isdisclosed. The method includes (1) fabricating an elongate shaft memberthat includes a proximal end section and a distal end section. In oneembodiment, the distal end section includes a nickel-titanium alloymember that has a first cross-sectional dimension (e.g., a thickness).The method further includes (2) dipping at least a portion of the distalend section in a molten solder material to apply (e.g., coat) the moltensolder material thereon, (3) cold working at least a portion of thedistal end section having the solder material coated thereon, whereinthe cold working yields a distal shapeable section having a linearpseudoelastic nickel-titanium microstructure, and (4) soldering thedistal shapeable section and a helical coil section disposed about thedistal shapeable section to an atraumatic cap without substantial lossof the linear pseudoelasticity of the distal shapeable section.

In one embodiment, fabricating an elongate shaft member that includes aproximal end section and a distal end section may include may includeattaching (e.g., by welding) a proximal end section fabricated from afirst material such as stainless steel to a distal end sectionfabricated from a second material such as nickel-titanium alloy.Alternatively, the elongate shaft member can be fabricated from a singlematerial such as, but not limited to, a nickel-titanium alloy.

In one embodiment, fabricating an elongate shaft member may furtherinclude drawing at least a portion of the elongate shaft member througha drawing die, rolling, calendaring, grinding, or combinations thereofto form or reshape the at least a portion of the elongate shaft memberand cleaning the elongate shaft member such as by ultrasonicallycleaning.

Ni—Ti alloys, such as those described herein, are very difficult tosolder due to the formation of a tenacious, naturally occurring oxidecoating which prevents the molten solder from wetting the surface of thealloy. It has been found that by first treating the surface of the Ni—Tialloy with molten alkali metal hydroxide, e.g., sodium, potassium,lithium or mixtures thereof to form a substantially oxide-free alloysurface and then pretinning (i.e., applying a suitable solder material,such as, a gold-tin solder, a gold-indium solder, a gold-germaniumsolder, a silver-tin solder, a silver-gold-tin solder, or anothersuitable solder) without contacting air, that Ni—Ti alloys can bereadily soldered in a conventional manner. In one embodiment, solder canbe applied to at least a portion of the distal end section by dippingthe at least the distal end section into a bath, wherein the bathincludes an upper layer of a molten metal hydroxide and a lower layer ofthe molten solder material. Alternatively, a layer of solder materialcan be applied to at least a portion of the distal end section bychemical vapor deposition (CVD), physical vapor deposition (PVD),sputter coating, and the like, and combinations thereof.

Subsequently, at least a portion of the distal end section, with thesolder material applied thereto, can be cold-worked to yield a distalshapeable end section having a second cross-sectional dimension. Afterapplying the solder material and cold working, a helical coil sectioncan be assembled around the a distal portion of the elongate shaftmember, including the distal shapeable section, and a rounded plug(i.e., an aturaumatic cap section) can be formed at the distal end ofthe assembly by soldering the distal shapeable section and a helicalcoil section disposed about the distal shapeable section to the roundedplug without substantial loss of the linear pseudoelasticity of thedistal shapeable section. The pretinning followed by cold working andforming the atraumatic cap at the distal end of the elongate shaftmember yields a user-shapeable distal end section that exhibits linearpseudoelastic deformation behavior without a phase transformation oronset of stress-induced martensite.

In a more specific embodiment, a method for fabricating a guide wiredevice that has a shapeable distal end section includes (1) providing anelongate shaft member that includes a proximal end section and a distalend section, wherein the distal end section includes a nickel-titaniumalloy member, (2) grinding at least a portion of the distal end sectionto a first cross-sectional dimension, and (3) ultrasonically cleaning atleast the distal end section. After grinding and cleaning, the methodfurther includes (4) dipping at least a portion of the distal endsection into a bath of a molten solder material, wherein the bath ofmolten solder material includes an upper layer of a molten metalhydroxide and a lower layer of the molten solder material, and (5) coldworking at least a portion of the distal end section, wherein the coldworking yields a distal shapeable section having a linear pseudoelasticnickel-titanium microstructure. After cold working at least a portion ofthe distal end section, the method continues with (6) ultrasonicallycleaning at least the distal end section, (7) disposing a helical coilsection about the distal shapeable section, and (8) forming anatraumatic cap section coupling the helical coil section and the distalshapeable section via a soldered joint, wherein the soldered joint isformed without loss of the linear elastic nickel-titaniummicrostructure.

Ni—Ti alloys, such as those described herein, are very difficult tosolder due to the formation of a tenacious, naturally occurring oxidecoating which prevents the molten solder from wetting the surface of thealloy in a manner necessary to develop a sound, essentially oxide free,soldered joint. It has been found that by first treating the surface ofthe Ni—Ti alloy with molten alkali metal hydroxide, e.g., a hydroxide ofsodium, potassium, lithium, or mixtures thereof to form a sufficientlyoxide free alloy surface and then pretinning with a suitable solder suchas a gold-tin solder or the like without contacting air, that the Ni—Tipiece can be readily soldered in a conventional manner.

A presently preferred alkali metal hydroxide is a mixture of about 59%KOH and about 41% NaOH. The solder may have a melting point temperaturein a range of about 150° C. to about 350° C. or about 280° C. to about300° C. The solder may contain from about 60 to about 85% gold and thebalance tin, with the presently preferred solder containing about 80%gold and about 20% tin. Other suitable solders may include gold-indium,gold-germanium, silver-tin, and silver-gold-tin.

In a presently preferred procedure, a multilayered bath is provided withan upper layer of molten alkali metal hydroxide and a lower layer ofmolten gold-tin solder. The part of the superelastic distal portion,which is to be soldered, is thrust into the multilayered bath throughthe upper surface of the molten alkali metal hydroxide which removes theoxide coating, leaving a sufficiently oxide free alloy surface, and theninto the molten solder which wets the cleaned surface. When the soldersolidifies upon removal from the molten solder into a thin coating onthe metal alloy surface, the underlying alloy surface is protected fromthe oxygen-containing atmosphere. Any of the alkali metal hydroxide onthe surface of the solder can be easily removed with water withoutdetrimentally affecting either the pretinned layer or the underlyingalloy surface. The pretinned Ni—Ti member is then ready for furtherprocessing and/or soldering. The pretinning procedure may be employedfor soldering other metal alloys having significant titanium levels.

In one embodiment, the distal end section may be drawn and ground to afirst dimension (e.g., about 0.08 mm), ultrasonically cleaned, andpretinned according to the method described above. In one embodiment,the distal end section can be dipped in the molten solder material atleast a second time if a thicker coating of solder is desired or if thedistal end section was not completely coated in the first dip. Afterpretinning, the distal end section is cold-worked, ultrasonicallycleaned, and soldered using conventional soldering procedures.

Suitable examples of cold working procedures that can be used to coldwork the distal end section include, but are not limited to, high forceflattening, stamping, rolling, calendaring, and combinations thereof.High force flattening is the currently preferred cold-working procedure.

The cold working procedure and the degree of cold working is importantfor obtaining a distal end section that is shapeable by a user. This isgraphically illustrated in FIG. 3 . FIG. 3 is a diagram schematicallyillustrating the relationship between degree of cold work andshapeability of a Ni—Ti alloy. As can be seen in FIG. 3 , whensuperelastic Ni—Ti has little or no cold work, the material has too muchsuperelastic character to be shaped. At the other end of the spectrum,Ni—Ti alloy material that has too much cold work becomes essentiallyunshapeable by manual means because its yield stress is too high. Thatis, highly cold-worked Ni—Ti alloy may be shapeable, but the stress thatmust be exceeded to exceed the elastic limit of the material (i.e., theyield stress) is too high to be conveniently shaped by hand. In themiddle of the spectrum, there is shown a region where the degree of coldwork is such that the Ni—Ti material is highly shapeable.

Specific examples of this phenomenon are illustrated in FIG. 4 , whichillustrates the yield stress of samples of Ni—Ti alloy having variousdegrees of cold work. The as-ground (0.08 mm) sample is illustrated atcurve 402. The superelastic, as-ground material cannot be permanentlydeformed with any degree of reliability. Curves 404-410 illustrate theeffect associated with increasing amounts of cold work. The sampleillustrated in curve 404 was flattened from the as-ground diameter ofabout 0.08 mm to about 0.045 mm, which corresponds to about 45% coldwork. The sample illustrated in curve 404 has a yield stress of about1200 MPa (˜175 ksi). The samples illustrated in curves 406 and 408 wereflattened from the as-ground diameter of about 0.08 mm to about 0.041 mmand 0.036 mm (respectively), which corresponds to about 49-55% coldwork. The samples illustrated in curves 406 and 408 have yield stressesof about 1900 MPa (˜275 ksi). The sample illustrated in curve 410 wasflattened from the as-ground diameter of about 0.08 mm to about 0.028mm, which corresponds to about 65% cold work. The sample illustrated incurve 410 has a yield stress of about 2070 MPa (˜300 ksi).

Based on the results illustrated in FIG. 4 , the distal shapeablesection can be cold-worked to have a yield stress in a range of about690 MPa (˜100 ksi) to about 2070 MPa (˜300 ksi) or about 1034 MPa (˜150ksi) to about 1380 MPa (˜200 ksi). Yield stresses in these ranges areobtained when the distal shapeable section that has a cold-workedmicrostructure that includes about 25% to about 65% cold work, about 40%to about 50% cold work, or about 45% cold work.

The linear pseudoelastic microstructure can be lost if the Ni—Timaterial is heated after cold working. This is illustrated in FIG. 5 ,which shows the progressive loss of linear pseudoelastic character ofNi—Ti alloy as a result of moderate heat exposure for varying amounts oftime. FIG. 5 illustrates the loss of cold work in three samples ofcold-worked Ni—Ti alloy having been exposed to 300° C. heat treatmentfor 2 minutes, 20 minutes, and 180 minutes. Curves in region 500 showmore linear pseudoelastic behavior, while curves in region 510 show moresuperelastic behavior. All curves show potentially significant loss ofcold work induced linear pseudoelastic behavior.

Comparing the results of FIGS. 4 and 5 , it is apparent why it isimportant to pretin and then cold work as opposed to cold workingfollowed by pretinning. That is, it can be seen that the yield stress isrelatively sensitive to the amount of cold work. For example, samples406 and 408 have relatively similar amount of cold work, yet their yieldstresses are considerably different. In order to obtain a distalshapeable section that can be reliable shaped, it is important tocarefully select the amount of cold work. On the flip side, it isimportant to not lose that cold work by pretinning after cold working.

While it is believed that pretinning after cold working may lead to lossof cold work, it is not believed that soldering leads to significantloss of cold work in the distal shapeable section. This is believed tobe due to the fact that soldering involves only localized applicationheat as opposed to solder dipping, which involves general application ofheat that could lead to potentially significant loss of cold workinduced linear pseudoelastic behavior.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed is:
 1. A method for fabricating a medical device, themethod comprising: fabricating an elongate shaft member that includes adistal end section, wherein the distal end section is formed of a distalnickel-titanium alloy member having a first cross-sectional dimension;applying a first layer of solder material to at least a portion of thedistal end section; following applying the soldering material, coldworking at least a portion of the distal end section having the soldermaterial applied thereto, wherein the cold working yields a distalpractitioner-shapeable end section in which the nickel-titanium alloy inthis cold worked region has linear pseudoelastic deformation behaviorwithout a phase transformation or onset of stress-induced martensite;and soldering the distal shapeable section and a helical coil sectiondisposed about the distal practitioner-shapeable section to anatraumatic cap without substantial loss of the linear pseudoelasticityof the distal practitioner-shapeable section; wherein the distalpractitioner-shapeable end section has a yield stress from about 100 ksito about 300 ksi.
 2. The method of claim 1, wherein the cold workingincludes at least one of high force flattening, stamping, rolling, orcalendaring.
 3. The method of claim 1, wherein the distalpractitioner-shapeable section exhibits 20% to 90% cold work.
 4. Themethod of claim 1, wherein the distal practitioner-shapeable sectioncomprises a cold-worked microstructure that includes 40% to 50% coldwork.
 5. The method of claim 1, further comprising applying a secondcoating of solder to at least a portion of the distal end section, overthe first layer of solder material, the second coating of solder being aseparately applied coating relative to the atraumatic cap.
 6. The methodof claim 1, wherein the cold-worked distal practitioner-shapeable endsection is in a martensitic phase.
 7. The method of claim 1, wherein themartensitic phase is substantially preserved in forming the solderedjoint.
 8. The method of claim 1, wherein the martensitic phase isstabilized by the cold working.
 9. The method of claim 1, wherein theelongate shaft member comprises stainless steel, a superelasticnickel-titanium alloy, or a combination thereof.
 10. The method of claim1, wherein the distal practitioner-shapeable end section has a yieldstress in a range from about 150 ksi to about 225 ksi.
 11. The method ofclaim 1, wherein the distal practitioner-shapeable end section has ayield stress in a range from about 150 ksi to about 200 ksi.
 12. Themethod of claim 1, the medical device further comprising a distalportion between a proximal end section and the distal end section,wherein the distal portion between the proximal end section and thedistal end section comprises a superelastic nickel-titanium alloy, andthe distal end section is linear pseudoelastic.
 13. The method of claim1, wherein a core of the distal end section surrounded by the soldermaterial consists of the linear pseudoelastic nickel titanium alloy. 14.A method for fabricating a medical device having a shapeable distal endsection, the method comprising: providing an elongate shaft member thatincludes a distal end section, wherein the distal end section is formedof a nickel-titanium alloy member; grinding at least a portion of thedistal end section to a first cross-sectional dimension; cold working afirst time at least a distal portion of the distal end section;ultrasonically cleaning at least the distal end section; dipping atleast a portion of the distal end section into a bath of a molten soldermaterial, wherein the bath of molten solder material includes an upperlayer of a molten metal hydroxide and a lower layer of the molten soldermaterial; following dipping at least a portion of the distal end sectioninto a bath of molten solder material, cold working a second time atleast a distal portion of the distal end section having the soldermaterial applied thereto, wherein the cold working yields a distalpractitioner-shapeable end section in which the nickel-titanium alloy inthis cold worked region has linear pseudoelastic deformation behaviorsuch that it is selectively shapeable; ultrasonically cleaning at leastthe distal end section; disposing a helical coil section about thedistal practitioner-shapeable section; and soldering the distalpractitioner-shapeable section and the helical coil section to anatraumatic cap without substantial loss of the linear pseudoelasticityof the nickel-titanium alloy in the distal practitioner-shapeablesection; wherein the distal practitioner-shapeable end section has ayield stress from about 100 ksi to about 300 ksi.
 15. The method ofclaim 14, further comprising that after dipping at least a portion ofthe distal end section into a bath of molten solder material, dipping asecond time at least a portion of the distal end section into a bath ofmolten solder material and thereby having a thicker coating of solder,the second coating of solder being a separately applied coating relativeto the atraumatic cap.
 16. The method of claim 14, wherein the upperlayer of molten metal hydroxide comprises molten potassium hydroxide,molten sodium hydroxide, or combinations thereof.
 17. The method ofclaim 14, wherein dipping at least a portion of the distal end sectioninto a bath comprises dipping at least a portion of the distal endsection in the molten solder material at a temperature in a range ofabout 150° C. to about 350° C.
 18. The method of claim 14, whereindipping at least a portion of the distal end section into a bathcomprises dipping at least a portion of the distal end section in themolten solder material at a temperature in a range of about 280° C. toabout 300° C.
 19. The method of claim 14, wherein the atraumatic capcomprises a cap of solder, wherein the solder comprises a eutecticalloy.
 20. The method of claim 14, wherein the helical coil section issecured to the distal portion at a proximal location and at anintermediate location.